When you buy or sell stock with an online broker when are the trading fees (approx. $7 or $10) deducted from your available balance? Is it when the order is placed? At the end of the month?
Typically the fees are charged when the order is executed.
The only catch I have ever ran into is when an order is partially executed. A good-till-cancel order that gets executed in several blocks over multiple days may get charged a separate commission for each day (but typically not each block).
If this is a simple brokerage account, you could avoid the whole question by using robinhood.com, which charges no commissions or maintenance fees.
As others have said, it depends on the brokerage firm.
My broker is Scottrade. With Scottrade the commission is assessed and applied the moment the order is filled. If I buy 100 shares of XYZ at $10 a share then Scottrade will immediately deduct $1007.02 out of my account. They add the commission and fees to the buy transaction. On a sale transaction they subtract the commission and fees from the resulting money. So if I sell 100 shares of XYZ at $11 a share I will get 1,092.98 put into my account, which I can use three business days later.